Magnesium implants were clinically used for the treatment of bone fractures by several surgeons back in the 1930s. For instance, J. Verbrugge (1934) used both, pure magnesium and Mg-8% Al alloy implants on 21 patients. However, after the Second World War, the use of magnesium as a resorbable implant material declined. In recent years, researchers have renewed their interest in resorbable magnesium implants. A main focus of magnesium research is the development of alloys and coatings. The major goals are to control the degradation rate, to avoid the formation of gas bubbles during degradation and to avoid potentially harmful alloying elements. Therefore, a need exists for magnesium alloys whose rate of degradation can be controlled and/or tuned as desired.
Commercial grade pure magnesium (3N—Mg) does not exhibit uniform degradation in vitro or in vivo. It is believed that the presence of impurities in the commercial product increases the degradation rate due to the formation of microgalvanic elements, including iron (Fe), copper (Cu) and nickel (Ni). Accordingly, a need exists for ultrapure magnesium material for medical applications, including surgical implants.
In order to forestall secondary phases, other contaminants such as cobalt (Co), silicon (Si), manganese (Mn) and aluminum (Al) also need to be controlled. Often times, the presence of a single contaminant can decrease the solubility limit of the other contaminants. The presence of these trace elements can shift the eutectic temperature within the magnesium phase diagram. During the solidification process, the contaminants can accumulate in the interdendritic spaces and induce the formation of secondary phases. These phases cannot be eliminated by subsequent thermomechanical treatments.
Embodiments of the present invention overcome one or more of above-noted challenges.